1. Field of the Invention
The present invention relates to an apparatus for compacting a metal powder into a gear blank such as a helical gear blank.
2. Description of the Related Art
It has been customary to manufacture gears for use in automobiles as sintered gears. FIG. 1 of the accompanying drawings shows one known powder compacting apparatus 51 for producing a compacted helical gear blank for use in automobiles.
As shown in FIG. 1, the powder compacting apparatus 51 comprises a horizontal lower plate 53 fixedly mounted on a foundation base 52, a horizontal floating plate 55 vertically slidably mounted on an intermediate portion of a vertical guide post 54 mounted on the foundation base 52 and floatingly supported by a floating mechanism (not shown), and an upper plate 56 vertically slidably engaging an upper end of the vertical guide post 54. A vertical lower punch 57 is mounted on the foundation base 52 and the lower plate 53. A floating die 58 is rotatably mounted on the floating plate 55. A vertical upper punch 59 is mounted on a horizontal punch holder plate 56a which is integrally mounted on the upper plate 56.
The lower punch 57 has external helical teeth p on its outer circumference, and the floating die 58 has internal helical teeth s on its inner circumference. The internal helical teeth s are held in mesh with the external helical teeth p.
The upper punch 59 comprises a vertical inner punch member 59b fixed to the punch holder plate 56a and a vertical outer punch member 59a disposed around the inner punch member 59b for rotation about its own axis. The outer punch member 59a has external helical teeth q on its outer circumference which can be held in mesh with the internal helical teeth s of the floating die 58.
The powder compacting apparatus 51 operates as follows: Initially, the upper punch 59 is in an elevated position. After a powdery material is filled in a die cavity space defined by the inner circumferential surface of the floating die 58 and the upper surface of the lower punch 57, the upper punch 59 is lowered to bring the external helical teeth q of the outer punch member 59a into mesh with the internal helical teeth s of the floating die 55. Upon continued downward movement of the upper punch 59, the upper punch 59 and the lower punch 57 compact the powdery material into a compacted helical gear blank W. As the upper punch 59 descends, the outer punch member 59a and the floating die 58 rotate about their axes to keep their helical teeth q, s out of interference with each other.
However, the powder compacting apparatus 51 suffers a disadvantage as described below. As shown in FIG. 2 of the accompanying drawings, the compacted helical gear blank W has different densities in the vertical direction. Specifically, the compacted helical gear blank W has a lower portion whose density is smaller than the density of an upper portion thereof.
It is therefore an object of the present invention to provide a powder compacting apparatus for producing a compacted helical gear blank which is free from density differences in the direction in which a powdery material is compacted into the compacted helical gear blank.
According to the present invention, there is provided a powder compacting apparatus comprising an upper punch having external helical teeth, a lower punch having external helical teeth, and a floating die is supported around the lower punch and having internal helical teeth meshing with the external helical teeth of the lower punch. The floating die and at least one of the upper and lower punches are rotatable about their own axes, the floating die and the lower punch jointly defining a die cavity space for being filled with a powdery material therein. The upper and lower punches are movable relatively toward each other to compact the powdery material in the die cavity space into a helical gear blank during a powder compacting process while the external helical teeth of the upper punch are meshing with the internal helical teeth of the floating die. The powder compacting apparatus has a floating die lowering mechanism for forcibly lowering the floating die a predetermined stroke with respect to the lower punch in a latter period of the powder compacting process.
If the floating die were not forcibly lowered, the helical gear blank being compacted would be caught by the internal helical teeth of the floating die. Therefore, upward reactive forces applied from the lower punch would not be sufficient, making the density of a lower portion of the helical gear blank smaller than the density of an upper portion of the helical gear blank. The floating die is forcibly lowered in order to increase the reactive forces from the lower punch.
When the floating die is forcibly lowered, even if the helical gear blank is caught by the internal helical teeth of the floating die, the helical gear blank is released from the internal helical teeth and has its lower surface reliably held against the upper surface of the lower punch. The lower punch can then apply sufficient upward reactive forces imposed on the helical gear blank which is being compacted between the upper punch and the lower punch.
The floating die lowering mechanism may comprise a presser rod for starting to lower the floating die when the upper punch is lowered a predetermined stroke.
The lower punch may be mounted on a lower plate, and the upper punch may be mounted on an upper plate, the upper plate being vertically movable toward the lower plate. A floating plate may be floatingly disposed between the upper plate and the lower plate, the floating die being mounted on the floating plate. The presser rod may be mounted on the upper plate and extend downwardly toward the floating plate.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.